1. The Field of the Invention
The present invention relates to systems and methods for enhancing the operation of rotating machinery. More specifically, the present invention relates to an imbalance compensator and an associated method of operation, by which an eccentric load on a driven shaft can be balanced to reduce vibrations and enhance the consistency of loading on the shaft.
2. The Relevant Technology
Rotating parts are common in many different types of machines. For example, most electric motors, internal combustion engines, transmissions, and the like include one or more rotating parts. Although rotating parts are often designed to be symmetrical, machining defects, wear, deformation, and the like often cause the center of gravity of the rotating part to be located some distance away from the axis of rotation. Thus, an eccentric load, or an imbalance, is created.
Eccentricity is often measured in terms of the magnitude of the eccentric load multiplied by the distance of the load from the rotational axis. Thus, eccentricity, or imbalance, may be stated in terms of foot pounds, gram centimeters, or the like.
Imbalanced loads are problematic for a number of reasons. They create vibrations that can cause noise, expedite wear, and potentially even result in failure of the machine, particularly where the frequency of vibration happens to match the natural frequency of some part of the machine. Additionally, imbalanced loads increase the mass moment of inertia of the rotating member, thereby placing a greater load on the driving mechanism. Furthermore, imbalanced loads can induce reciprocating stresses, or xe2x80x9cfatiguexe2x80x9d stresses in the machine. Fatigue stresses also tend to accelerate wear and failure of machine parts.
Imbalanced loads are particularly problematic for mechanized tools and other machines in which wear of a rotating member occurs rapidly. For example, mills, lathes, drill presses, grinders, and the like rotate tools or workpieces that will experience wear during the machining process. Unfortunately, wear may not necessarily occur evenly about the circumference of the tool or workpiece. Thus, even if the machine is well made and balanced prior to use, imbalanced loads will rapidly appear.
In response to these problems, a number of balancing devices have been created. Although known devices have been helpful in reducing load imbalances in some cases, known balancing devices tend to fall short in a number of ways. For example, many known balancing devices are somewhat complex, and are therefore expensive to manufacture and maintain.
Additionally, many known balancing devices have a somewhat limited range of compensation capability. Thus, they can only be effectively used in applications in which the magnitude of the imbalance is known to be within a certain range. Some balancing devices can be adjusted prior to use, for example, by installing additional weights or removing weights. Such devices cannot dynamically cover a wide range; rather, once an out of-spec imbalance occurs, the machine must be stopped so that the necessary adjustments can be made.
Some known balancing devices provide compensation by moving a gas, for example, through the use of thermal gradients. Unfortunately, gases are not very dense; consequently, a large volume of gas must be moved to provide compensation. The temperature gradients required to keep such volumes in place are difficult to maintain because the temperature within the balancing device tends to even itself out over time through heat transfer from heated parts of the device to those that must remain unheated to maintain the temperature gradient.
A further problem with known balancing devices is that many are simply too large to fit within the space constraints of certain machines. The amount of imbalance a given device can compensate for is dependent upon the size of the device. Some machines simply have a load imbalance/available space ratio that is too high to permit the use of existing balancing devices.
Yet further, many known devices have a limited resolution. For example, some devices have only a limited number of positions in which weights can be moved to provide compensating weight. Thus, the balancing device is unable to fully compensate for any load imbalance that falls between the levels the device is designed to counteract. Hence, the device""s ability to fine tune the load balancing is severely limited.
Still further, many known devices are quite heavy. The weight of the balancing device adds to the overall weight of the machine, and also adds to the rotational inertia of the entire rotating system. Consequently, the system cannot start or stop rotation as rapidly as would be possible without the balancing device.
Accordingly, a need exists for an imbalance compensator capable of compensating for comparatively large load imbalances, without requiring a great deal of space around the rotating shaft. A further need exists for an imbalance compensator that is capable of such large scale correction without sacrificing the resolution required for fine tuning. Yet further, a need exists for an imbalance compensator that adds comparatively little weight and rotational inertia to the rotating machine. Still further, a need exists for an imbalance compensator that is comparatively simple in design and manufacture, so that the imbalance compensator can be inexpensively produced and easily adapted to different rotational systems.
The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available balancing devices. The present invention provides an imbalance compensator with enhanced compensation range and resolution, with a comparatively lightweight, compact, and simple design.
According to one configuration, the imbalance compensator comprises a balancing ring positioned around a rotating shaft, and attached to rotate with the shaft. The balancing ring may be controlled by a ring controller positioned near the balancing ring to provide control signals and power through magnetic transmission. The ring controller, in turn, may be connected to a control console that contains circuitry pertinent to the operation of the imbalance compensator and provides a user interface. The control console may also be connected to a vibration sensor mounted at a location near the shaft and oriented to measure the shaft""s vibration.
The balancing ring may be embodied in several different forms. In certain embodiments, the balancing ring has a housing with a generally annular shape. An interior opening of the housing is large enough to fit around the shaft with clearance. The housing contains a receiving coil positioned near the outer diameter of the housing. The receiving coil is connected to a processor to transmit control and power signals to the processor. Additionally, a phase sensor and a vibration sensor are also connected to the processor to relay data concerning the rotational orientation and vibration of the shaft and balancing ring to the processor.
The processor processes the vibration and phase data to determine which direction the center of gravity of the balancing ring must move to compensate for the load imbalance. The center of gravity of the ring should be moved in a direction substantially opposite that of the load imbalance, with respect to the axis of rotation of the shaft.
According to one embodiment, the processor is connected to a plurality of actuators installed in the housing. Each actuator is connected to a solid compensation mass, in the form of a compensation ring, to apply a force tending to push the solid compensation mass in a certain direction with respect to the axis of rotation of the shaft. The actuators may be axisymmetrically arrayed around the compensation ring to impinge against the compensation ring from opposing directions, thereby providing the capability to relatively move the compensation ring and housing in any direction within the plane perpendicular to the shaft.
Each actuator may take a variety of forms, one of which is a linear actuator containing a piezoelectric force crystal. Electric signals from the processor induce expansion of the piezoelectric crystal. The linear actuators may each have a movable core oriented toward the compensation ring; expansion of each crystal then moves the associated movable core to push the compensation ring. The compensation ring can be moved with respect to the housing by increasing the force exerted by the linear actuators on one side of the shaft, while decreasing the force exerted by the linear actuators on the opposite side of the shaft.
Each movable core may have a distal end that directly contacts the compensation ring. In the alternative, the movable cores may each be connected to some type of mechanical transfer device that transmits the force of the movable core to the compensation ring. For example, each of the movable cores maybe pivotally connected to a lever arm that is also pivotally attached to the housing. A distal end of the lever arm may then abut against the compensation ring. The lever arm provides a mechanical advantage that can be used to alter the displacement and force of the movable core to provide the proper combination of force and displacement against the compensation ring. These embodiments move the center of gravity of a single compensation ring away from the axis of rotation in a direction opposite the load imbalance to provide compensation.
The receiving coil may receive the power and control signals in the form of a magnetic transmission from the ring controller. The ring controller may therefore have sending coil configured to provide a time-varied magnetic field, a portion of which travels through the receiving coil.
According to other embodiments, a single chamber containing a fluid is used to move the center of gravity of the balancing ring. The chamber may have a generally annular shape. The fluid may then take the form of a magnetic fluid, with low magnetic reluctance particles suspended or otherwise contained within a nonmagnetic carrier fluid. The magnetic particles may be denser than the carrier fluid. Thus, the center of gravity of the magnetic fluid may be moved by subjecting a portion of the magnetic fluid to a magnetic field, thereby attracting the heavier magnetic particles to the portion of the fluid under the influence of the magnetic field.
The magnetic field may be provided in several different ways. According to one embodiment, a plurality of electromagnets are mounted within the housing and axisymmetrically distributed about the outer periphery of the chamber. One or more of the electromagnets may be selectively activated to create one or more fields on the side of the chamber opposite the load imbalance. The magnetic field or fields attract particles to move the center of gravity of the fluid to compensate for the load imbalance. As with the embodiment containing the mechanical actuators, power and control signals maybe received through the use of a receiving coil positioned toward the outer diameter of the housing, in combination with a sending coil within the ring controller.
In the alternative, the electromagnets may be positioned within the ring controller, which remains stationary while the balancing ring rotates. The housing therefore need only contain the chamber with the magnetic fluid; the center of gravity of the magnetic fluid may be manipulated through the use of the stationary electromagnets. For example, the ring controller may include timing circuitry configured to time the activation of the electromagnets to coincide with rotation of the shaft. Thus, the magnetic fields produced by the electromagnets remain at the same orientation with respect to the shaft to consistently compensate for the load imbalance.
In such an embodiment, the processor and phase sensor may also be positioned within the ring controller. Thus, no information need be transmitted between the balancing ring and the ring controller. Consequently, the receiving and sending coils may not be necessary.
According to another embodiment, the magnetic field in the chamber maybe created through the use of a plurality of carts positioned to move in a circular path concentric with the chamber. For example, the housing may contain a gear ring surrounding the chamber, with teeth on the inside diameter of the gear ring. The carts may each have two sprockets with teeth sized to mesh with those of the gear ring. Each cart may contain a motor to drive one or both sprockets, and a coil with which the cart can receive power and control signals.
Each cart may also have a pin that fits within a track positioned just within the gear ring. Each cart may also have a permanent magnet adjacent to the outer diameter of the chamber. The carts may be powered and directed through the use of a control coil of the housing, encircling the gear ring. Each cart then creates a magnetic field within the chamber and thereby attracts magnetic particles to its current position. The carts are moved via signals sent from the processor to the cart through the control coil. The carts may be moved close to each other to provide a high degree of imbalance compensation, or they may be positioned comparatively far apart for more minor adjustment of the center of gravity of the balancing ring.
A processor, phase sensor, and receiving coil may once again be positioned within the housing, so that the balancing ring can receive control signals and power from the ring controller. The control coil may be integrated with or positioned near the receiving coil.
According to additional alternative embodiments, the housing may have a plurality of fluid-containing chambers. The fluid need not be a magnetic fluid, but is preferably a somewhat dense liquid. The fluid maybe pumped from one chamber to the next through the use of one or more mechanical pumps, or pumps that move fluid through the use of moving solid parts. Preferably, the pump or pumps take the form of micropumps manufactured through the use of MEMS (microelectromechanical systems) manufacturing processes. The pumping action may concentrate fluid in one or more chambers substantially opposite the imbalance direction. The chambers in which fluid is concentrated are heavier than the other chambers, and therefore provide an eccentric weight to compensate for the load imbalance.
In one configuration, a number of micropumps equal to the number of chambers may be utilized. Each micropump may be connected to two adjacent chambers through the use of conduits so that fluid is pumped in circular fashion to reach the chambers in which the fluid is to be concentrated. As with other embodiments, the housing contains a receiving coil, phase sensor, and processor that can be used to energize and control the micropumps.
In the alternative, only a single micropump may be used. The micropump may be connected to two aggregate conduits, each of which branches into conduits leading to about half of the chambers. Each conduit may have a valve to selectively permit or restrict fluid flow through the conduit. Thus, fluid may be transferred between two chambers connected to different aggregate conduits by opening one valve connected to each aggregate conduit, closing the remaining valves, and activating the micropump. To transfer fluid between two chambers fed by the same aggregate conduit, fluid may simply be transferred to a chamber fed by the other aggregate conduit, and then back to the chamber to be filled.
Through the use of the systems and methods presented herein, a comparatively large counterbalancing mass may be moved to compensate for larger imbalance loads, without making the imbalance compensator unduly heavy or unwieldy. Additionally, the counterbalancing mass may generally be adjusted in comparatively small increments to provide fine tuning of the imbalance compensation. Furthermore, the imbalance compensators may be comparatively easily manufactured and installed within a compact space.
These and other features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.